Ruck Elizabeth C, Nakov Teofil, Alverson Andrew J, Theriot Edward C
Department of Biological Sciences, University of Arkansas, 1 University of Arkansas, SCEN 601, Fayetteville, AR 72701, USA.
Department of Biological Sciences, University of Arkansas, 1 University of Arkansas, SCEN 601, Fayetteville, AR 72701, USA.
Mol Phylogenet Evol. 2016 Oct;103:155-171. doi: 10.1016/j.ympev.2016.07.023. Epub 2016 Jul 22.
The Surirellales and Rhopalodiales are large, widespread, and morphologically diverse groups of raphid pennate diatoms (Bacillariphyta) whose raphe, a structure that facilitates active motility, opens internally into a siliceous canal. We collected 202 representatives of the lineage and sequenced genes from the nuclear, plastid, and mitochondrial genomes to infer phylogenetic relationships as a basis for comparative study of ecology and morphological evolution as well as reclassification. The lineage was ancestrally marine, and we report the first evidence for a 'stepping stone' model of marine-freshwater transitions in which freshwater invasions were preceded by adaptation to intermediate brackish habitats. Phylogenetic comparative analyses also showed that the shift from an apical (e.g., Entomoneis) to transapical major axis of development (e.g., Surirella) did not have to proceed through subcircular intermediate forms (i.e., Campylodiscus). Rather, subcircular forms evolved both within lineages with longer apical axis or longer transapical axis. We also used the inferred phylogeny as a basis for genus-level reclassification of the lineage. Campylodiscus now includes the fastuosoid members of Surirella and Campylodiscus, but excludes other marine Campylodiscus which are now classified as Coronia. Surirella includes the Surirella striatula clade, Surirella Pinnatae group, and species formerly classified as Cymatopleura. We resurrected the genus Iconella to accommodate Stenopterobia and the robustoid members of Surirella and Campylodiscus. We broadened Epithemia to include members of the paraphyletic genus Rhopalodia. Finally, we discuss the challenges of constructing a classification that best leverages available phylogenetic data, while minimizing disruption to the research community and recognizing practical considerations stemming from the slow rate of progress on systematic studies of understudied organisms.
双菱藻目（Surirellales）和杆状藻目（Rhopalodiales）是大型、分布广泛且形态多样的具脊羽纹硅藻（硅藻门）类群，其假沟（一种有助于主动运动的结构）在内部通向硅质管。我们收集了该谱系的202个代表物种，并对核基因组、质体基因组和线粒体基因组中的基因进行测序，以推断系统发育关系，作为生态学和形态进化比较研究以及重新分类的基础。该谱系起源于海洋，我们报告了首个关于海-淡水过渡“踏脚石”模型的证据，即在淡水入侵之前先适应了中间咸淡生境。系统发育比较分析还表明，从顶端（如Entomoneis）到跨顶端主轴发育（如双菱藻）的转变不一定必须通过近圆形中间形式（即弯盘藻属Campylodiscus）。相反，近圆形形式在具有较长顶端轴或较长跨顶端轴的谱系中都有进化。我们还将推断出的系统发育关系作为该谱系属级重新分类的基础。弯盘藻属现在包括双菱藻属和弯盘藻属中具显著特征的成员，但不包括其他现在被归类为Coronia的海洋弯盘藻属物种。双菱藻属包括条纹双菱藻分支、羽纹双菱藻组以及以前被归类为波缘藻属的物种。我们恢复了Iconella属，以容纳窄翅藻属以及双菱藻属和弯盘藻属中粗壮型的成员。我们扩大了Epithemia属，将并系的杆状藻属成员纳入其中。最后，我们讨论了构建一个能最佳利用现有系统发育数据的分类体系所面临的挑战，同时尽量减少对研究群体的干扰，并认识到由于对研究不足的生物体进行系统研究进展缓慢而产生的实际问题。
